For processing a raw material such as a vegetable or fruit into dry powder the process has been accomplished in the prior art by the process steps shown in the flow chart of FIG. 1. The process is accompanied by the following problems:
1) A large number of components and controls have been required due to the separate function of each individual component and control for each operational unit together with the necessary insertion of handling devices and buffer tanks between them.
2) The operation of such a large number of components and controls is labor intensive and involves considerable preventative maintainence.
3) Additionally the prior art arrangements require a higher capital investment and a relatively large operational site due to the installation of such a large number of components and controls.
4) The costs for the administration and operation of the aforementioned equipment is considerable.
5) A deterioration of the quality of the product is due to the process steps of cutting and slicing, handling and crushing of the raw materials due to air oxidation.
6) Due to the extended period of each handling and drying process step, the productivity is low and as such decreases the resultant quality of the product.
7) Product quality deterioration occurs due to the generation of heat during the crushing operation.
8) The processing components are sustained by the position of and the clinging thereto of the process material during the handling operation after the spraying thereon of the liquid additives.
9) Since the injection of the processing gas is carried out generally at ordinary pressure, there is some difficulty in obtaining sufficient permeation into the interior of the material being processed.
10) By gas injection, an objectionable odor is generated in the process material.
11) A preservative is employed for increasing the preservability or the durability of a food product as a whole, together with the primary raw materials of such food products. Many root crops possess a potential for being employed as preserved edible foods, however, root crops in general have irregular sizes and shapes and are not easily processed into commercial products. They are usually supplied from agricultural firms without the removal of petioles and stalks which have been discarded hitherto due to a lack of any viable processing technique even though they possess, in many cases, potential for being used also as preserved edible foods.
In order to accommodate the general demand for using a raw crop material as a preserved edible food, it has been necessary to process the raw material into a dry powdery form. In conventional techniques for such processing however, a deterioration of the quality of the product has occurred so that the product becomes unsuitable as a preserved edible food.
A preserved edible food is in itself a food product and should additionally have the properties of being preserved as well as the intrinsic properties of such food products, such as nutritional value, favorable taste, fragrance, biofuntionality controlling activity and so on. Thus, it is necessary for processing the raw material into a dry pulverous product to avoid any decomposition of the effective components of the raw material by heat or by oxidation during the drying process step and to prevent any deterioration of the product hue and fragrance.
Any deterioration in such properties will be increased when the temperature is higher and when the duration of exposure to the given temperature is longer. It is desirable to carry out the drying operation at a temperature which is as low as possible and for a duration which is as short as possible. However, in practice, many factors should be considered. For example, there are many possibilities including complex combinations of conditions, such as each specific raw material employed, the contemplated products quality, temperature, processing duration and so on. Also, choosing a practical operation among the various techniques of higher temperature/short period and lower temperature/long period present many possibilities.
Arrangements have been proposed in the prior art to improve the quality and to prevent the deterioration thereof, including a proposal for low temperature and shorter processing periods.
Technical means have been previously proposed for cutting the raw cut material into small sizes for facilitating the drying thereof by increasing the effective surface area of evaporation. Also agitation of the raw material and the elevation of the processing temperature have previously been employed generally with a view to attaining a short drying period. These measures exhibit a positive contribution by seeking to preserve the favorable properties of the raw material by the rapid drying thereof. However, a negative contribution has been introduced due to the mechanical processing of the raw material.
Freeze drying is superior in preserving the original properties of the raw crop material but is costly due to the high installation and operational costs. Therefor, freeze drying has found its application only in situations where other techniques can only be employed with difficulty.
Drying by hot air, which has been widely employed tends to suffer from an increase in cost relative to both installation and operation of the process where thermal deterioration of the product quality of the product is to be avoided. Such is the case because the operation of the process should be attained by warmer air at a relatively low temperature. There is a certain inherent limitation in achieving the prevention of deterioration of the product quality by oxygen and by heat even by operating in an optimum combination of drying temperature and drying time.
Drying by radiation such as irradiation by infrared or microwave radiation may be effective for short periods but, nevertheless, the product is liable to suffer from deterioration of product quality due to an increase in the temperature of the material by the heat generated therein.
Finally, vacuum drying which is useful for the prevention of deterioration of product quality due to the oxidation by air requires a longer period of time for the completion of the process. Such longer period has resulted in the installation of a large scale plant which increases operational costs for the heating and the maintainence of the vacuum.
One of the frustrating problems experienced in the standard techniques resides in the choice of which device or apparatus in view of the balance between the product quality, installation investment and operation costs. Such is so because, as discussed above, each drying technique has its own advantages and drawbacks.
The term "crusher" as employed herein, means a device for carrying out a primary crushing or rough crushing that attains production of "powder" product but not an ultrafine powder. However, there are a large variety of crushing devices each adapted for a specific purpose.
In order to prevent deterioration of the product quality, employment of a process having a shorter duration and lower temperature is essential. This requires cooling of the material during the processing, since any crushing is carried out by the generation of heat. Moreover, the crushing should be accomplished under an inert atmosphere or under vacuum for avoiding quality deterioration by oxidation. Though the crushing of the raw material does not constitute any critical process step, a product of higher quality will be obtained thereby. Low temperature vacuum crushing can be achieved at a cost comparable with conventional arrangements so long as the requirements for product quality are compromised with the installation cost.